The Linux Programming Interface

1080 Chapter 52

notification has occurred. At this point, the process will have been deregis-

tered for message notification.

b) Call mq_notify() to reregister this process to receive message notification u.

c) Execute a while loop that drains the queue by reading as many messages as

possible i.

Listing 52-6: Receiving message notification via a signal

––––––––––––––––––––––––––––––––––––––––––––––––––––––pmsg/mq_notify_sig.c

#include <signal.h>

#include <mqueue.h>

#include <fcntl.h> /* For definition of O_NONBLOCK */

#include "tlpi_hdr.h"

#define NOTIFY_SIG SIGUSR1

static void

handler(int sig)

{

/* Just interrupt sigsuspend() */

}

int

main(int argc, char *argv[])

{

struct sigevent sev;

mqd_t mqd;

struct mq_attr attr;

void *buffer;

ssize_t numRead;

sigset_t blockMask, emptyMask;

struct sigaction sa;

if (argc != 2 || strcmp(argv[1], "--help") == 0)

usageErr("%s mq-name\n", argv[0]);

q mqd = mq_open(argv[1], O_RDONLY | O_NONBLOCK);

if (mqd == (mqd_t) -1)

errExit("mq_open");

w if (mq_getattr(mqd, &attr) == -1)

errExit("mq_getattr");

e buffer = malloc(attr.mq_msgsize);

if (buffer == NULL)

errExit("malloc");

r sigemptyset(&blockMask);

sigaddset(&blockMask, NOTIFY_SIG);

if (sigprocmask(SIG_BLOCK, &blockMask, NULL) == -1)

errExit("sigprocmask");